1. Field of the Invention
The present invention relates to a power window system for an automobile, and in particular, to a power window system with a control unit for detecting a foreign object caught in a car window for the purpose of stopping or reversely operating to open or close the window when the foreign object is caught in the car window.
2. Description of the Prior Art
A power window system for opening and closing windows by a driving unit (motor) is used on an automobile. A power window system is proposed in which, when a foreign object is caught in a car window during opening or closing operation of the window, it is judged whether a foreign object is caught in the window, and if something is caught in the window, the motor is immediately stopped or reversely operated for the purpose of avoiding overload on the motor and of protecting what is caught in the window.
A conventional type power window system as described above comprises, as shown in FIG. 4, a driving unit 41 (hereinafter referred as xe2x80x9cmotorxe2x80x9d) rotatable in normal and reverse directions to open or close the window, a power feeding unit 42 for supplying power to the motor 41, an operation switch unit 43 having a plurality of switches and for outputting voltage serving as a signal for opening or closing the window by manual operation, a control unit 44 (hereinafter referred as xe2x80x9cCPUxe2x80x9d) for controlling rotation of the motor 41 via the power feeding unit 42 in response to operation of the operation switch unit 43, and a pulse generator 45 for generating repeated pulses accurately in response to the rotation of the motor 41.
When one of switches (43a, 43b, 43c and 43d) on the operation switch unit 43 is operated, a signal corresponding to the operated switch is inputted to one of input terminals (P02, P03 or P04) of the CPU 44. In response to the inputted signal, the CPU 44 outputs a signal from output terminals (P05 or P06) to the power feeding unit 42. The power feeding unit 42 supplies power to the motor 41 in response to the inputted signal. As a result, the motor 41 is rotated in a normal or reverse direction, and the window is opened or closed.
In the arrangement as described above, when the motor 41 is rotated, the pulse generator 45 is operated in response to the rotation of the motor 41, and one-phase pulses, being reversed at each half turn, are generated, and the pulses are outputted to the input terminal P07 of the CPU 44. In this case, the CPU 44 finds out interval of rising/falling of the inputted pulses from the count of an internal clock signal. The count value thus obtained is converted to a motor torque value, and this is compared with a value already set in an internal memory. If the motor torque value is greater than the preset value, it is judged that a foreign object is caught in the window, and the motor 41 is stopped or reversely operated.
Also, an alternative method has been used. In this method, the interval of generation of the inputted pulses is converted to moving speed of the window, and when the moving speed is decreased, it is judged that a foreign object is caught in the window. That is, when the amplitude of a pulse becomes longer, it is judged that a foreign object is caught in the window, and the motor 41 is stopped or reversely operated.
However, when the power window system is started, operation of the motor 41 is not stable until a certain time period elapses. In association with instable operation, sudden changes may occur in a motor torque or in a current value, and it is not possible to detect in stable manner that a foreign object is caught in the window. In this respect, in the conventional type power window system, no detection of a foreign object is achievable for a certain period after the starting of the motor 41, e.g. from the time of starting of the motor 41 up to the time of generation of 40 pulses, and the foreign object caught in the window is detected thereafter. In this respect, even when a foreign object is caught in the window during the above period, it is not possible to detect the trouble. According to another method, it is judged that a foreign object is caught in the window when an interval of pulse generation is 700 ms or more, for instance. Thus, some time is required from the time when a foreign object is caught in the window to the time of judgment. As a result, the foreign object is continuously caught in the window without being removed during this period.
To solve the above problem, it is an object of the present invention to provide a power window system, by which it is possible to reliably detect in a short time that a foreign object is caught in the window even during the period from the starting of the motor to the moment when the motor reaches stable operation.
To attain the above object, the power window system according to the present invention comprises a driving unit rotatable in normal and reverse directions to open or close a car window, a pulse generator for generating repeated pulses in response to the operation of the driving unit, and a control unit for judging that a foreign object is caught in the window based on the repeated pulses and for stopping or reversely operating the driving unit, wherein in a first period (i.e. from the starting of the driving unit to a first time point when the window starts upward movement), the control unit judges and detects that a foreign object is caught in the window when time duration in which pulses are generated in one of a second cycle or a third cycle is longer than a given multiple of time duration required for the repeated pulses in a first cycle immediately before.
Also, the present invention provides the power window system as described above, wherein, in a second period (i.e. from the first time point to a second time point when the window reaches and maintains operation at a constant speed), the control unit judges and detects that a foreign object is caught in the window when time duration in which pulses are generated in one of the second cycle and the third cycle is longer than time duration required for the first cycle.
Further, the present invention provides the power window system as described above, wherein, in a third period after the second time point, the control unit judges and detects that a foreign object is caught in the window when time duration in which pulses are generated in the second cycle is longer than a given multiple of time duration in which the pulses are generated in the first cycle, and also when time duration in which pulses are not generated in the second cycle is longer than a given multiple of time duration in which pulses are not generated in the first cycle.